Absorbent Article with Colour Changing Properties

ABSTRACT

An absorbent article such as a diaper, a pant diaper, a sanitary napkin, an incontinence guard etc., which includes thermochromic fibres. The thermochromic fibres may be incorporated in one or more of the following components of the absorbent article: the inner coversheet, the acquisition layer, the absorbent structure, the outer coversheet or a layer arranged between the outer coversheet and the absorbent structure. The article may alternatively contain a fibrous layer which mainly or entirely contains thermochromic fibres. The thermochromic fibers may be used as wetness indicator, as a fever indicator, as a function control for microorganisms that have been incorporated in the article or for amusement purposes, such as creating colour imprints of hands etc.

TECHNICAL FIELD

The present invention refers to an absorbent hygiene article such as adiaper, a pant diaper, a sanitary napkin, an incontinence guard etc.having colour changing properties at a selected temperature.

BACKGROUND OF THE INVENTION

The concept of indicating wetness in an absorbent article, especially adiaper, by a wetness indicator, which by a colour change indicates thepresence of body fluid in the diaper, is previously known.

Thus a wetness indicating diaper is known through U.S. Pat. No.5,197,958 provided by printing a pattern by a thermochromic ink on theexterior surface of the outer coversheet of a diaper. This pattern ofthermochromic ink becomes visible or changes colour when a selectedtemperature is exceeded, adapted to indicate that the diaper has beenwetted by body fluid.

EP-A-0 347 657 discloses a wetness indicating hot-melt adhesive whichchanges colour in response to the presence of moisture. The hot-meltadhesive contains particles of a dyestuff which is insoluble in theadhesive composition, but which are soluble in water. The hot-meltadhesive can be used in a diaper as a wetness indicator.

U.S. Pat. No. 5,167,652 discloses a moisture sensitive film produced byblending a copolyester with a moisture absorbing copolyamide. The filmturns white when wetted. The film may be used as a diaper backsheet toindicate when the diaper has been wetted.

There is however a continuing need for improvement and for moresophisticated ways of indicating an increase or decrease in temperaturein an absorbent article above a selected threshold value, for example inorder to indicate the presence of body fluid, to indicate fever of thewearer or for visual and to enhance the customer product perception.Alternatively it may be desired to make a welding pattern more visibleby means of a differing colour.

OBJECT AND MOST IMPORTANT FEATURES OF THE INVENTION

An object of the present invention is to provide a solution to theproblems set out above and to suggest an absorbent article having colourchanging properties with a high degree of flexibility when it comes tothe choice of where and how the colour changing means is placed in thearticle. The process of incorporating the colour changing means in thearticle should further be simple. These and further objects haveaccording to the invention been solved by the fact that that saidabsorbent article comprises thermochromic fibres.

The thermochromic fibres may be incorporated in different parts andcomponents of the article. Thus in one aspect of the invention they areincorporated in the outer coversheet and/or a layer arranged between theouter coversheet and the absorbent structure.

According to one embodiment the outer coversheet comprises a fibrouslayer containing at least 1% by weight, preferably at least 5%, morepreferably at least 10% by weight and most preferably from 20 to 70% byweight, of said colour changing fibres, based on the weight of saidfibrous layer in areas in which said thermochromic fibres aredistributed. Thus if the thermochromic fibres are distributed in only ina limited area of a layer, the above concentrations should be calculatedonly on this limited area.

An entire layer may also consist of thermochromic fibres as the solefibrous material, in which case the basis weight of such a layer shouldbe at least 10 g/m², preferably at least 15 g/m².

Depending on what colour is used different amounts of thermochromicfibres in the layer may be used. For example for a yellow colour ahigher amount of thermochromic fibres may be needed than for a blackcolour. In general the amount of thermochromic fibres should besufficient to indicate a colour change.

In a further embodiment the fibrous layer containing the thermochromicfibres forms the external garment facing side of the outer coversheet.

In a still further embodiment the absorbent structure containsthermochromic fibres. According to one aspect of the invention theabsorbent structure comprises at least 1% by weight, preferably at least10% by weight and more preferably at least 20% by weight, of saidthermochromic fibres, based on the total weight of said absorbentstructure in areas in which said thermochromic fibres are distributed.

In a further aspect of the invention the absorbent article comprises aliquid pervious bodyside liner which contains thermochromic fibres.

In a still further aspect of the invention the article further comprisesa liquid acquisition layer placed between the bodyside liner and theabsorbent structure, wherein said acquisition layer containsthermochromic fibres.

In one embodiment of the invention the thermochromic fibres changecolour at a temperature of between 25 and 43° C., preferably between 30and 38° C.

In a further embodiment the article comprises at least two differenttypes of thermochromic fibres having different colours and/or differenttrigger temperatures.

The invention further refers to the use of thermochromic fibres as awetness indicator in an absorbent article. In this case it is preferredthat the thermochromic fibres are incorporated in one or more of thefollowing components of the absorbent article: the absorbent structure,the outer coversheet, a layer arranged between the outer coversheet andthe absorbent structure and an acquisition layer.

Thermochromic fibres may further be used for enhance the customerproduct perception, and to increase the interaction between the user andthe product, such as give play and learn features. One example would beto create colour imprints of hands etc. in an absorbent article. In thiscase the thermochromic fibres are incorporated in the outer coversheetof a diaper or pant diaper.

In a further embodiment thermochromic fibres are used as a feverindicator of a wearer of an absorbent article, wherein the thermochromicfibres are incorporated in one or more of the following components ofthe absorbent article: the inner coversheet, the acquisition layer andthe absorbent structure.

In another aspect of the invention thermochromic fibres are used as afunction control of microorganisms, for example Lactobacillus, added toan absorbent article, wherein the thermochromic fibres are incorporatedin one or more of the following components of the absorbent article: theinner coversheet, the acquisition layer and the absorbent structure. Thethermochromic fibres should in this case change colour at a temperatureof at least 40° C., preferably at least 50° C. The change of colourshould be irreversible.

In a further embodiment thermochromic fibres are contained in an elasticmaterial, for example an elastic laminate which in some parts has beede-elastified by heat treatment, ultrasonic welding or the like.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in the following in greater detail byway of examples and with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic perspective view of a diaper.

FIG. 2 is a section according to the line II-II in FIG. 1.

FIG. 3 is a schematic perspective view of a pant diaper.

FIG. 4 is a schematic view of a sanitary napkin or incontinence guard.

DEFINITIONS Absorbent Article

The term “absorbent article” refers to products that are placed againstthe skin of the wearer to absorb and contain body exudates, like urine,faeces and menstrual fluid. The invention mainly refers to disposableabsorbent articles, which are articles that are not intended to belaundered or otherwise restored or reused as an absorbent article afteruse.

Inner Liquid Permeable Cover

The inner liquid permeable cover forms the inner cover of the absorbentarticle and in use is placed in direct contact with the skin of thewearer. The inner liquid permeable cover can comprise a nonwovenmaterial, e.g. spunbond, meltblown, carded, hydroentangled, wetlaid etc.Suitable nonwoven materials can be composed of natural fibers, such aswoodpulp or cotton fibres, manmade fibres, such as polyester,polyethylene, polypropylene, viscose etc. or from a mixture of naturaland manmade fibres. The inner liquid permeable cover material mayfurther be composed of tow fibres, which may be bonded to each other ina bonding pattern, as e.g. disclosed in EP-A-1 035 818. Further examplesof inner liquid permeable cover materials are porous foams, aperturedplastic films, laminates of film/nonwovens etc. The materials suited asinner liquid permeable cover materials should be soft and non-irritatingto the skin and be readily penetrated by body fluid, e.g. urine ormenstrual fluid. The inner liquid permeable cover may further bedifferent in different parts of the absorbent article.

Outer Liquid Impermeable Cover

The outer liquid impermeable cover forms the outer cover of theabsorbent article at least on the core area thereof. The outer liquidimpermeable cover can comprise a thin plastic film, e.g. a polyethyleneor polypropylene film, a nonwoven material coated with a liquidimpervious material, a hydrophobic nonwoven material, which resistsliquid penetration, or a laminate, e.g. of a plastic film and a nonwovenmaterial. The outer liquid impermeable cover material may be breathableso as to allow vapour to escape from the absorbent structure, whilestill preventing liquids from passing through. Examples of breathableouter liquid impermeable cover materials are porous polymeric films,nonwoven laminates from spunbond and meltblown layers, laminates fromporous polymeric films and nonwoven materials.

Absorbent Structure

The “absorbent structure” is the absorbent structure disposed betweenthe two covers of the absorbent article. The absorbent structure can beof any conventional kind. Examples of commonly occurring absorbentmaterials are cellulosic fluff pulp, tissue layers, highly absorbentpolymers (so called superabsorbents), absorbent foam materials,absorbent nonwoven materials or the like. It is common to combinecellulosic fluff pulp with superabsorbent polymers in an absorbentstructure. Superabsorbent polymers are water-swellable, water-insolubleorganic or inorganic materials capable of absorbing at least about 20times its weight of an aqueous solution containing 0.9 weight percent ofsodium chloride. Organic materials suitable for use as a superabsorbentmaterial can include natural materials such as polysaccharides,polypeptides and the like, as well as synthetic materials such assynthetic hydrogel polymers. Such hydrogel polymers include, forexample, alkali metal salts of polyacrylic acids, polyacrylamides,polyvinyl alcohol, polyacrylates, polyacrylamides, polyvinyl pyridines,and the like. Other suitable polymers include hydrolyzed acrylonitrilegrafted starch, acrylic acid grafted starch, and isobutylene maleicanhydride copolymers and mixtures thereof. The hydrogel polymers arepreferably lightly crosslinked to render the material substantiallywater insoluble. Preferred superabsorbent materials are further surfacecrosslinked so that the outer surface or shell of the superabsorbentparticle, fiber, flake, sphere, etc. possesses a higher crosslinkdensity than the inner portion of the superabsorbent. The superabsorbentmaterials may be in any form suitable for use in absorbent compositesincluding particles, fibers, flakes, spheres, and the like.

A high absorption capacity is provided by the use of high amounts ofsuperabsorbent material. For an absorbent structure comprising a matrixof hydrophilic fibers, such as cellulosic fibers, and superabsorbentmaterial, the proportion of superabsorbent material is preferablybetween 10 and 90% by weight, more preferably between 30 and 70% byweight.

It is conventional in absorbent articles to have absorbent structurescomprising layers of different properties with respect to liquidreceiving capacity, liquid distribution capacity and storage capacity.The thin absorbent bodies, which are common in for example baby diapersand incontinence guards, often comprise a compressed mixed or layeredstructure of cellulosic fluff pulp and superabsorbent polymers. The sizeand absorbent capacity of the absorbent structure may be varied to besuited for different uses such as for infants or for adult incontinentpersons.

Acquisition Layer

A so called acquisition layer may be arranged between the inner liquidpermeable cover and the absorbent structure. The acquisition layer isadapted to quickly receive and temporarily store discharged liquidbefore it is absorbed by the underlying absorbent structure. Suchacquisition distribution layers are well known in the art and may becomposed of porous fibrous waddings or foam materials.

Themochromic Fibres

Thermochromic pigments are organic compounds that effectuate areversible or irreversible colour change when a specific temperaturethreshold is crossed. A thermochromic pigment basically comprises threemain components: (i) an electron donating colouring organic compound,(ii) an electron accepting compound and (iii) a solvent reaction mediumdetermining the temperature of the colouring reaction to occur.

A thermochromic particulate material which may be used according to theinvention may be prepared from particles of a non-thermoplastic resinhaving enclosed therein the three components of electron-donatingchromogenic substance, electron-accepting substance and solvent bycoating the particles with a hydrophilic high-molecular-weight compound.The thermochromic particulate material, when incorporated into a vinylchloride plastisol, remains free of the influence of the plasticizer,stabilizer, lubricant or the like contained in the plastisol and retainsvery high stability even when heated.

The process for preparing a molded product of thermochromic polyvinylchloride is characterized by incorporating a thermochromic particulatematerial into a vinyl chloride plastisol comprising a vinyl chlorideresin, plasticizer, stabilizer, lubricant and filler. Thereafter moldingthe resulting mixture. The thermochromic particulate material beingprepared from particles of a non-thermoplastic resin having encapsulatedtherein the three components of electron-donating chromogenic substance,electron-accepting substance and solvent by coating the particles with ahydrophilic high-molecular-weight compound.

A molded thermochromic polyvinyl chloride material can thereby beprepared which reliably undergoes a reversible color change with achange of temperature. A material like this becomes skin-colored whenthe temperature rises beyond about 40° C. The color change isreversible. This is further described in U.S. Pat. No. 4,826,550.

Such thermochromic pigments and the mechanism bringing about thetemperature triggered colour change to occur are well-known in the artand are for example described in U.S. Pat. No. 4,826,550 and U.S. Pat.No. 5,197,958.

Thermochromic or temperature sensitive colour changing fibres are knownfrom the textile field to be used in clothing, sport equipment etc. Thefibres are either produced by blending a thermochromic pigment in thebase resin from which the fibres are to be produced, for example apolyolefin, such as polyethylene or polypropylene, polyester, polyvinylalcohol etc. or by using a thermochromic colouring liquid for thefibers. The production of temperature sensitive colour-changing fibresare disclosed in for example JP2002138322 and JP2001123088. The fibreschange colour at a selected temperature. The change of colour is eitherreversible or irreversible.

An example of a fiber which can be used according to the invention is athermochromic fiber which is partly characterized in that the flexuralmodulus of elasticity of a base resin is within the range of 300-1,500MPa in the temperature-sensing color-changing fiber. The fiber is formedby melt blending a thermally color-changing pigment in a dispersed statein the base resin of a polyolefin resin and/or the polyolefin resinblended with a thermoplastic resin. This fiber is earlier used in thetextile field. The inventors have found that fibers with thischaracteristics may also be suited for use in absorbent articles,especially diapers. The fiber is further described in JP 2002-138322.

In another embodiment of the invention the thermochromic fiber is athermosensitive color-changing acrylic synthetic fiber. Such fibers maybe constituted of a plurality of long fibers or short fibers of athermosensitive color-changing synthetic acrylic fiber having 1-100 μmouter diameter of monofilament. The fibers may be formed by dispersing0.5-40 wt. % of a thermosensitive pigment containing essential threeingredients of (A) an electron donating coloring organic compound, (B)an electron-accepting compound and (C) a reaction solvent determiningthe occurrence temperature of a coloring reaction of the ingredients Aand B. This is describes in more detail in JP 2001-055623.

Another thermochromic fiber according to the invention is a conjugatefiber which is excellent in reversible color changeability, brightnessand durability. It may be produced by using a (1) thermal color changingpolyester composed of a thermal color changing material-containingthermoplastic polyester and (2) a fiber-forming polyester in which ≧50mol % of an acid component is terephthalic acid; 0-50 mol % thereof isisophthalic acid and ≧70 mol % of a diol component is composed ofbutanediol and/or hexanediol are subjected to melt conjugate spinning.The resultant yarn is then drawn to afford the objective fiber which isconjugate fiber, containing a part composed of the component (1) joinedto a part composed of the component (2) and having ≧1.5 g/denier fiberstrength, ≦80% fiber elongation and ≦25% shrinkage factor in boilingwater. This is further described in JP 4241115.

Another fiber which is excellent in friction durability and mechanicalcharacteristics which may be suitable for the invention can be achievedby using a low-melting thermoplastic resin containing atemperature-sensitive color changing granular substance as a corecomponent and a high-melting thermoplastic resin as a sheath componentat a specific ratio.

The fiber is obtained by mixing an acid developing substance (e.g.3,3′-dimethoxyfluoran) with an acidic substance (e.g. phenol) and asolvent (e.g. octyl alcohol), granulating the resultant mixture andcarrying out conjugate spinning of a thermoplastic resin (e.g.polypropylene), having ≦230° C. melting point and containing 1-40 wt. %resultant temperature-sensitive color changing granular substance. Thegranules having 1-50 μm grain diameter and ≧200° C. heat resistance as acore component and a thermoplastic resin (e.g. nylon) having ≦280° C.melting point as a sheath composition at (1/9)-(9/1) weight ratio ofcore component:sheath component, having a smooth surface and excellentin mechanical characteristics with a high level of temperature-sensitivecolor changing function. This method is further described in JP 3161511.

The temperature sensitive pigment used in the thermochromic fibers haspreferably an average particle size of 0.5-50 μm, preferably 0.5-30.0,even more preferably μm 0.5-15.0 μm measured by appropriate ASTDMstandard method.

The thermosensitive pigment may preferably be of a microcapsule typewhich is known in the art of thermosensitive pigments.

DESCRIPTION OF PREFERRED EMBODIMENTS

The absorbent article shown in FIG. 1 is in the form of a diaper 1having a longitudinal, y, and a transverse direction, x, and comprises,as seen in its longitudinal direction, a front portion 2, a back portion3 and a crotch portion 4 there between. In its most common form thediaper comprises an absorbent structure 5 and a cover enclosing theabsorbent structure. Said cover comprises an inner liquid pervious cover6 on the wearer facing side of the absorbent structure 5 and an outerliquid impervious cover 7 on the garment facing side of the absorbentstructure. The outer cover may in one embodiment comprise a liquidimpervious plastic film 7 and a nonwoven layer 15 on the garment facingside of the film. The inner liquid pervious cover 6 is often referred toas topsheet, while the outer liquid impervious cover 7 is often referredto as backsheet. An acquisition layer 8 is arranged between the innerliquid pervious cover 6 and the absorbent structure 5.

The inner cover 6 and the outer cover 7 extend outward beyond theperipheral edges of the absorbent structure 5 and have their innersurfaces bonded to each other, e.g. by gluing or welding by heat orultrasonic. The inner and outer cover materials may further be bonded,e.g. by adhesive, to the absorbent structure.

The areas of the article adjacent the leg openings are along thelongitudinal side edges provided with elastic members 9 which are bondedbetween the inner cover 6 and the outer cover 7 material layers in astretched condition so as to provide elasticized leg openings of thediaper. Corresponding elastic members are arranged to extend in thetransverse, x, direction in the front 2 and back portion 3 adjacent thetransverse side edges forming the waist opening of the diaper.

The back portion 3 is provided with fasteners 10 attached thereto. Thefasteners are intended to be fastened to the front region of the articleto form a pant-like shape. The fasteners 10 may be in the form ofadhesive tapes or hook elements adapted to attach to a loop material,for example in the form of a nonwoven material forming the outercoversheet of the diaper.

FIG. 3 shows a so called pant diaper in which the front and backportions 2 and 3 are joined to each other along their longitudinal sideedges thereof forming side seams 11, to define a waist-opening 12 and apair of leg-openings 13. The front and back portions 2 and 3 are joinedalong said side seams 11, for example by adhesive, ultrasonic welding,heat sealing or the like. The front and back portions 2 and 3 may bejoined along said side seams with the inner cover 6 facing inwards, asis shown in the drawings. Alternatively they are joined in an overlappedmanner with the inner cover 6 of either the front or back portion facingthe outer cover 7 of the opposite region.

In an alternative form the pant diaper comprises a core regioncomprising the absorbent structure, a liquid pervious inner cover and aliquid impervious outer cover as disclosed above, and a chassis regionoutside the core region, wherein the chassis region comprises acoversheet of a soft and comfortable material, for example an elasticlaminate. An example of such a pant diaper is disclosed inPCT/SE2004/001004.

The waist area, at least a part of the leg opening area and the sideareas adjacent the side seams 11 are elasticized. The elastification isusually accomplished by a plurality of elastic members, such as elasticthreads 14, contractably affixed in a stretched condition between theouter cover 7 and the inner cover 6. Alternatively elastic materials,such as an elastic laminate, may be used to form the chassis of thearticle in those areas where elasticity is desired.

FIG. 4 shows a further embodiment in the form of an incontinence guardor sanitary napkin intended to be worn in the panties of a wearer.

The absorbent articles shown in the drawings are only examples of somecommon types of personal care absorbent articles and the invention maybe applied to any type of absorbent articles falling under thedefinition given above.

The absorbent article according to the present invention containsthermochromic fibres. As mentioned above thermochromic fibres are fibreshaving incorporated therein a thermochromic pigment. The thermochromicpigment basically comprises three main components. (i) an electrondonating colouring organic compound, (ii) an electron accepting compoundand (iii) a solvent reaction medium determining the temperature of thecolouring reaction to occur.

Such thermochromic pigments and the mechanism bringing about thetemperature triggered colour change to occur are well-known in the artand are for example described in U.S. Pat. No. 4,826,550 and U.S. Pat.No. 5,197,958. The first mentioned document discloses molded products ofpolyvinyl chloride, having incorporated therein thermochromicparticulate material. The last mentioned document discloses a wetnessindicating diaper having a thermochromic ink printed on the diaperbackhseet.

A description of fibers having incorporated therein such thermochromicpigments can be found in any of the following Japanese published patentapplications: JP 2002-138322 disclosing thermally colour-changing fibresfor various textile applications, such a imitated wool; JP 2001-123088disclosing a reversibly thermochromic colouring liquid for fibers andfabrics made therefrom; JP 2001-055623 disclosing thermosensitivecolour-changing synthetic acrylic fibres; and JP 8027653 disclosing athermally colour-changing nonwoven material containing a certain amountof reversibly colour-changing crimped fibres.

The thermochromic pigment may be incorporated in the base resin of thefibers in the form of microcapsules or as a colouring liquid for thefibres.

The entire fiber may be coloured by the thermochromic pigment, or thefiber may be of a bicomponent type, wherein either the core or the outercasing of the fiber is provided with the thermochromic pigment. Thechange of colour may either be reversible or irreversible.

The thermochromic fibers may, depending on the intended purpose of thethermo-chromic function, be incorporated in any suitable component ofthe absorbent article, such as the outer liquid impermeable cover, alayer arranged between the absorbent structure and the outer cover, theabsorbent structure, a layer of an absorbent structure, the inner liquidpervious cover or the acquisition layer.

Thermochromic fibers having a change of colour at a temperature slightlybelow body temperature, or in the interval from about 30 to about 37°C., may be used as a wetness indicator indicating the presence of bodyfluid, when incorporated in for example the absorbent structure 5, theouter coversheet 7, 15, a layer arranged between the outer coversheetand the absorbent structure 5 or in the acquisition layer 8. They mayalso be incorporated in a nonwoven outer garment facing layer 15,outside a liquid impervious plastic film, of the outer coversheet, sincethe thin plastic film is normally sufficiently thermally conductive toallow the temperature to rise on the outer surface thereof when thearticle is wetted with body fluid.

They may further be used as a fever indicator, when incorporated in theinner coversheet 6, the acquisition layer 8 or the absorbent structure5. In this case the thermochromic fibres should have a change of colourat an interval slightly above normal body temperature, or in theinterval from about 37.5 to about 39° C.

Thermochromic fibres incorporated in the outer coversheet 7, 15 may alsobe used for amusement purposes and something for the baby to play with,such that when the baby puts his/her hand on the diaper an imprint ofthe hand in the form of different colour will occur for a while, butdisappear again, in the case of reversible thermochromic fibers.

Thermochromic fibres may further be incorporated in an elastic material,for example an elastic laminate which in some parts has beede-elastified by heat treatment, ultrasonic welding or the like. Theelastic material may be an elastic nonwoven, a laminate of nonwoven andfilm or a nonwoven laminate. The thermochromic fibers in thede-elastified portions will change colour triggered by the heattreatment or ultrasonic welding, so as to indicate wherede-elastification has occurred. The elastic laminate may form part of anabsorbent article, for example elastic side panels of a diaper or pantdiaper.

One further use of thermochromic fibers is as a function control ofLactobacillus or other microorganism incorporated in for example theinner coversheet 6, the acquisition layer 8 and/or the absorbentstructure 5. This is done by indicating whether a certain temperature,above which the microorganism looses its function, has been exceededduring transport and storage. The thermochromic fibres should in thiscase change colour at a temperature of at least 40° C., preferably atleast 50° C. The change of colour of the thermochromic fibres should inthis case be irreversible.

The thermochromic fibers may be incorporated substantially homogeneouslyin an entire layer and mixed with other fibers in the layer.Alternatively they are inhomogeneously incorporated only in parts of alayer. A further alternative is that a separate fibrous layer, forexample a nonwoven layer, produced mainly (at least 50%) or evenentirely from thermochromic fibres as the sole fibrous component isincorporated in the article. An appropriate amount of the thermochromicfibres in for example an inner coversheet, an acquisition layer, anabsorbent structure or a layer in an absorbent structure or an outercoversheet, is at least 1% by weight, preferably at least 5%, morepreferably at least 10% by weight and most preferably from 20 to 70% byweight based on the weight of said fibrous layer in areas in which saidthermochromic fibres are distributed. Thus if the thermochromic fibresare distributed in only half of the layer, the weight-% should be basedon the weight of that half part of the layer.

The rest of the fibres, with which the thermochromic fibres are mixed,may vary depending on which component of the absorbent article thethermochromic fibres are incorporated in, if it for example is abacksheet material, a coversheet, a backsheet or an absorbent structure.Thus the rest of the fibres may be cellulosic fibres, polyethylene,polyproplyene, polyester, polylactide, viscose fibres and the like.

In one embodiment the rest of the fibres with which the thermochromicfibres are mixed are made of the same polymeric material as thethermochromic fibres. Thus if the thermochromic fibres comprisespolypropylene having a thermochromic pigment incorporated therein, thesethermochromic fibres may be mixed with other polypropylene fibres withno thermochromic pigment in them.

In case a fibrous layer consisting of thermochromic fibres as the solefibrous component is used, such layer should have a basis weight of atleast 7, preferably at least 10 and more preferably at least 15 g/m².

Two or more types of thermochromic fibres may be used in the samearticle. These different thermochromic fibres may have different coloursand/or different trigger temperatures.

The time it takes for the colour change to occur may at least for someapplications be of importance. For example it may be desired that thechange of temperature occurs in less than 3 seconds, preferably in lessthan 2 seconds and more preferably in less than 1 second from when thefibres have been exerted to the trigger temperature. A high impacttemperature (high above the trigger temperature) on the thermochromicfibres will give a faster colour change than a low impact temperature(close to the trigger temperature).

It is pointed out that the present invention is not limited to theembodiments described above and shown in the drawings, but that aplurality of modifications are possible within the scope of the claims.

1-24. (canceled)
 25. An absorbent hygiene article comprising anabsorbent structure and a liquid impervious outer coversheet, whereinsaid absorbent article comprises thermochromic fibres, in which athermochromic pigment is blended with a resin from which the fibers areproduced.
 26. The absorbent article as claimed in claim 25, wherein saidouter coversheet or a layer arranged between the outer coversheet andthe absorbent structure contains the thermochromic fibres.
 27. Theabsorbent article as claimed in claim 26, wherein said outer coversheetcomprises a fibrous layer containing at least 1% by weight of saidthermochromic fibres, based on the weight of said fibrous layer in areasin which said thermochromic fibres are distributed.
 28. The absorbentarticle as claimed in claim 26, wherein said outer coversheet comprisesa fibrous layer having a basis weight of at least 7 g/m², containingthermochromic fibres as the sole fibrous component.
 29. The absorbentarticle as claimed in claim 27, wherein said fibrous layer containingthe thermochromic fibres forms an external garment facing side of theouter coversheet.
 30. The absorbent article as claimed in claim 25,wherein said absorbent structure contains the thermochromic fibres. 31.The absorbent article as claimed in claim 30, wherein the absorbentstructure comprises at least 1% by weight of said thermochromic fibres,based on the weight of said absorbent structure in areas in which saidthermochromic fibres are distributed.
 32. The absorbent article asclaimed in claim 31, wherein said absorbent structure comprises afibrous layer having a basis weight of at least 7 g/m², containingthermochromic fibres as the sole fibrous component.
 33. The absorbentarticle as claimed in claim 25, further comprising a liquid perviousinner coversheet, wherein said inner coversheet contains thermochromicfibres.
 34. The absorbent article as claimed in claim 33, furthercomprising a liquid acquisition layer placed between the innercoversheet and the absorbent structure, wherein said acquisition layercontains thermochromic fibres.
 35. The absorbent article as claimed inclaim 33, wherein said liquid pervious inner coversheet or saidacquisition layer contains at least 1% by weight of said thermochromicfibres, based on the weight of said layer in areas in which saidthermochromic fibres are distributed.
 36. The absorbent article asclaimed in claim 33, wherein said liquid pervious inner coversheet orsaid acquisition layer comprises a fibrous layer having a basis weightof at least 7 g/m², containing thermochromic fibres as the sole fibrouscomponent.
 37. The absorbent article as claimed in claim 25, wherein thethermochromic fibers change colour at a temperature of between 25 and40° C.
 38. The absorbent article as claimed in claim 25, wherein saidarticle comprises a fibrous layer which contains thermochromic fibres asthe sole fibrous component, said fibrous layer having a basis weight ofat least 7 g/m².
 39. The absorbent article as claimed in claim 25,wherein said article comprises at least two different types ofthermochromic fibers having different colours or different triggertemperatures.
 40. A method of indicating wetness in an absorbentarticle, the method comprising: blending a thermochromic pigment with aresin to produce a plurality of thermochromic fibers; and including thethermochromic fibers in the absorbent article.
 41. The method as claimedin claim 40, wherein the thermochromic fibres are incorporated in theouter coversheet of a diaper or pant diaper.
 42. The method as claimedin claim 40, wherein the thermochromic fibres are incorporated in one ormore of the following components of the absorbent article: an absorbentstructure, an outer coversheet, a layer arranged between the outercoversheet and the absorbent structure, and an acquisition layer. 43.The method of claim 40, further comprising creating colour imprints ofhands in an absorbent article to enhance the customer productperception.
 44. A method of indicating a fever in a wearer of anabsorbent article, the method comprising: blending a thermochromicpigment with a resin to produce a plurality of thermochromic fibers; andincluding the thermochromic fibers in the absorbent article.
 45. Amethod of controlling microorganisms in an absorbent article, the methodcomprising: blending a thermochromic pigment with a resin to produce aplurality of thermochromic fibers; and including the thermochromicfibers in the absorbent article.
 46. A method of indicatingde-elastification of a portion of an absorbent article, the methodcomprising: blending a thermochromic pigment with a resin to produce aplurality of thermochromic fibers; and including the thermochromicfibers in the absorbent article.